The White Dragontail. A butterfly in Hong Kong

AJP saw about a dozen of these butterflies around a big bush in Tai Po Kau last week. They are White Dragontails (Lamproptera curius), a species which occurs throughout south-east Asia. They have short wings and buzz around like wasps.

Python eats pig. But how does the python cope with all the calcium in the pig’s bones? A new study discovers an entirely new mechanism and a new type of intestinal cell

During the 1990s the Burmese Python (Python bivittatus) hit the headlines because of research done by Stephen Secor and Jared Diamond in Los Angeles. Secor was a postdoc in Diamond’s lab. Jared Diamond is of course the polymath who had three simultaneous careers: as a physiologist (in which capacity we have twice given invited papers at the same conference*); as an ornithologist and ecologist working in New Guinea; and as a student of the history of the human environment as exemplified by his book, Guns Germs, and Steel which earned him the Pulitzer Prize.

Burmese Python
Photographed at Bardiya National Park, Nepal
by Shadow Ayush
Creative Commons Attribution-Share Alike 4.0 International

This highly productive research line became possible because of advances made in the previous twenty years, largely by amateur herpetologists, in breeding snakes in captivity. This is one example of the upside of the commercial breeding of this species to be set against the awful practice of propagating colour varieties and the establishment of the Burmese Python as an invasive species in Florida.

Ambush predatory snakes like pythons spend long periods without food. Between their infrequent meals they shut down and reduce in size their digestive systems. But when food is caught, constricted and swallowed whole there is a burst of activity. The gut, liver etc grow rapidly while other organs like the heart are also involved in the rapid shift to digestion. Cardiac output—the volume of blood pumped per minute—increases to a greater extent than during exercise. This pioneering research has been continued by Stephen Secor, latterly at the University of Alabama, along with a number of collaborators.

When a snake ingests a whole animal, it gets the entire skeleton as well the nutrients contained in the other tissues. In other words it has to deal with very large amounts of calcium and phosphorus. 

Although calcium plays a key part in providing strength to such structures as birds’ eggs, bone, and mollusc shells the process of biocalcification has long been of great interest simply because formation of these high-calcium structures and secretions, like milk, have to take place against a background of a low concentration of calcium in blood and a very much lower concentration inside cells. The concentrations are closely regulated and an excess in either compartment can be deadly even though large quantities of calcium have to pass through the cell involved in building the calcium-rich structures.

The latest discovery is described in a paper in Journal of Experimental Biology by Jehan-Hervé Lignot of the University of Montpelier, Robert Pope, an electron microscopist who also worked in France, and Stephen Secor. They found specialised cells in the intestinal epithelium that are involved in the production of calcium and phosphorus particles. The particles are released back into the gut and expelled as part of the faeces. In fasting snakes, the cells had no particles. Similarly, the cells of snakes fed meat bone-free sausages had no particles. However, when a calcium supplement was added the the bone-free sausages particles were present, as of course they were in snakes fed whole mice and rats.

Are the specialised cells in some way trapping excess calcium before it reaches the blood circulation? Or are they an excretory route activated by an excess calcium in blood? Clearly though, they are involved in removing calcium at times of excess input.

This is one of the photomicrographs from the paper
by Lignot et al 2025.
B. Alizarin red staining of a histological section
of the proximal intestine. Arrow indicates a particle
stained with Alizarine Red S. Scale bar: 100µm

The authors have also found the particles in other snakes and in the Gila Monster. However, there have been no reports of such cells in the intestines of other vertebrates that ingest vertebrate prey whole. The question then of course is anybody looked, especially at times of really excessive calcium intake such that which could be obtained by supplemental feeding of calcium. They concluded:

It would be of great value to monitor a large-scale analysis within vertebrates that eat the entirety of their bony prey in order to identify how broadly distributed this cell type could be within the animal kingdom. Is it an ancestral cell type that remained within some snakes and lizards, or a modified enterocyte that could be highly plastic in nature? The presence of this cell type in fasting snakes with typically an empty crypt cell suggests that this is a specific cell type.

Amen to that.

*The first was exactly 55 years ago on the day I was drafting this article last week

Lignot J-H, Pope RK, Secor SM. 2025. Diet-dependent production of calcium- and phosphorus-rich‘spheroids’ along the intestine of Burmese pythons: identification of a new cell type? Journal of Experimental Biology 228, jeb249620. doi:10.1242/jeb.249620

Mexico 2025: A Potoo or Two

Returning in the dark from a boat trip along the Rio La Tovara near San Blas on the Pacific Coast of Mexico, there were lots of snags—dead or dying trees without a top—and most held a Northern Potoo (Nyctibius jamaicensis). Instead of sitting motionless on the trunk as they do all day these birds were awake on on the lookout for large flying insects.

What I had not realised is that these birds sit with their very large eyes pointed upwards. They were clearly looking for large insects flying above them thus mounting their ambush from below rather than from above.

The Northern Potoo occurs from Mexico to Costa Rica in Central America, together with some Caribbean islands including, as the specific name implies, Jamaica.

Their entire lives are spent on branches or in the air. A single egg is laid on a bare broken branch and the young is cared for there by both parents.

Humpback Whales: the full behavioural works off Puerto Vallarta, Mexico

What sort of whale watching were we in for we wondered when we landed at Puerto Vallarta on the Pacific Coast of Mexico. We went out into Banderas Bay on two consecutive mornings and found out. It was not the usual sightings of whales ploughing through the sea and then diving ‘tail-up’. This was the full works, especially on the second morning. The Humpbacks (Megaptera novaeangliae) are in the bay from December until March. That population moves north to feed in the Pacific between Russia and North America.

Female Humpbacks and their newly-born young stay in the shallow water at the north end of the bay. Males hang about waiting for the females, with young in tow, to move out of the shallows when coming into their first oestrus post partum. A female may have a pretty permanent male ‘escort’ who may or may not strike it lucky if he can outdo the band of pursuing, barging males.

We saw the males do the full range of their behavioural repertoire from slapping the surface of the water with their fins or tail, flapping water sideways with their tail and breaching. Our breaching count went up rapidly from one (out of the blue before breakfast while anchored off Pitcairn island near the site of the remains of HMS Bounty in 2010) to what must have been more than ten.

There are all sorts of explanations for male Humpbacks breach, from display to shifting skin parasites. My impression—which may be entirely wrong—is that we were witnessing a gigantic aquatic lek within hearing and sight of the females, including those in the shallow water. In other words, my splash is noisier and thus bigger than his so I am the best hope for you to pass on your genes this time round. Oh, and look at how strong my fins are.

We saw one male emerge from the water and snapping its mouth shut as if feeding (see the video below). There have been occasions when the humpbacks have been seen feeding on shoals of small fish in Banderas Bay but in general they live, and the females lactate, using only stored fat and protein. 

We moved to quieter water in highly recommended the Ecotours boat Prince of Whales for the hydrophone to pick up the song of the males. You can hear some of that and see the whales in the video below. After seeing the males flopping back into the water after virtually the whole body had risen out of it, and imagining the effect it would have had on bone and muscle, there was the suggestion from the gentlemen on board that is was no wonder whales wail.

After whales, dolphins, birds nesting on islands in the bay it was off to lunch and birdwatching in the afternoon.

A band of White-nosed Coatis in Mexico

Shortly after crossing the 470 metre long suspension bridge at El Jorullo a few miles inland from Puerto Vallarta on the Pacific Coast of Mexico a small café on the forest track comes into view. Standing outside for a few minutes to see if the noisy Military Macaws would come into view, a group of White-nosed Coatis (Nasua narica) appeared, obviously wondering if we were going to have something to eat and give into their entreaties for a few scraps from the table. Having just had lunch we weren’t but they tried their luck for a while before disappearing back into the forest of Canopy River Park. Members of the Carnivora they may be but these, like other members of the procyonid family, like raccoons, are very much omnivorous.

Except in the breeding season, the bands are said to comprise only females and juveniles, the make leading a solitary existence. They are diurnal.

White-nosed coatis are very much a species of Central America, occurring from parts of Arizona and New Mexico in the north to the very tip of Colombia in the south.

Herons in the Mangroves: Mexico in February

Rio La Tovara near San Blas on the Pacific Coast of Mexico

On our last day before leaving Mexico we had a boat trip at 4 pm which took us from our hotel in San Blas first to the mouth of the Rio Arroyo Grande and then through the mangroves lining the narrow Rio La Tovara. Night fell as cruised upstream and we returned in the dark. On the way out we saw a number of birds in the mangroves, including the three species of heron shown below. Even in daylight it was dark under the mangroves.

   This Tricolored Heron Egretta tricolor was moving slowly on the lookout for fish

  Green Heron Butorides virescens also on the hunt

  Boat-billed Heron Cochlearius cochlearius. One of a small group.
They often feed by night and eat anything that moves, from mammals to shrimps

As darkness fell Snowy (Egretta thula) and Great (Ardea alba) Egrets were gathered to roost

Seeing the aptly named Boat-billed Herons was appropriate seeing we were staying at a hotel—an excellent hotel—with the same name: the Garza Canela.

A Good Summer for Garden Butterflies

 Small Copper Lycaena phlaeas

Painted Lady Vanessa cardui

Small Tortoiseshell Aglais urticae

Red Admiral Vanessa atalanta

The stars of the show this year with up to seven in the garden at any one time. Feeding on nectar and then the fallen over-ripe plums.